X-ray diagnosis apparatus for feeding an x-ray tube having a rotary anode

ABSTRACT

An X-ray diagnosis apparatus for feeding an X-ray tube having a rotary anode for illumination and exposure with means for setting the exposure data and a feeding device for the motor of the rotary anode, is particularly characterized by means releasing an exposure during the high running of the rotary anode when the lowermost speed of the anode at which the exposure current of the X-ray tube is permissible and the desired heating current of the X-ray tube have been reached.

United States Patent Winkler 1 Nov. 4, 1975 1 X-RAY DIAGNOSIS APPARATUS FOR 3,244,884 4/1966 McLaughlin 250/406 FEEDING AN X RAY TUBE HAVING A 3,546,461 12/1970 Craig 250/416 ROTARY ANODE Inventor: Hans-Werner Winkler, Buckenhof,

Germany Assignee: Siemens Aktiengesellschaft, Munich,

Germany Filed: Sept. 23, 1974 Appl. No.: 508,405

Related US. Application Data Continuation-in-part of Ser. No. 371,444, June 19,

US. Cl 250/402; 250/406 Int. Cl. HOSG 1/70 Field of Search 250/401, 402, 406, 416

References Cited UNITED STATES PATENTS 10/1965 Teague 250/406 Primary ExaminerCraig E. Church Attorney, Agent, or FirmRichards & Geier [57] ABSTRACT An X-ray diagnosis apparatus for feeding an X-ray tube having a rotary anode for illumination and exposure with means for setting the exposure data and a feeding device for the motor of the rotary anode, is particularly characterized by means releasing an exposure during the high running of the rotary anode when the lowermost speed of the anode at which the exposure current of the X-ray tube is permissible and the desired heating current of the X-ray tube have been reached.

2 Claims, 2 Drawing Figures US. Patent Nov. 4, 1975 3,917,949

TADHUGENERATUR lass F|G.2

X-RAY DIAGNOSIS APPARATUS FOR FEEDING AN X-RAY TUBE HAVING A ROTARY ANODE This application is a continuation-in-part of a pending patent application, Ser. No. 371,444, filed June 19, 1973.

This invention relates to an X-ray diagnosis apparatus for feeding an X-ray tube having a rotary anode for illumination and exposure with means for setting the exposure data and a feeding device for the motor of the rotary anode.

In known X-ray diagnosis devices of this type an exposure is released after the motor for the rotary anode has been switched on and when the rotary anode has reached its highest speed. This time period can be comparatively long when high output X-ray tubes with high anode speeds are used and this has a disturbing effect when going. over from illumination to exposure.

In use it is desired to keep the transmission time period from illumination to exposure as short as possible. This transmission time period is essentially determined by the dimensions of the rotary anode motor, so that a diminishing of this time period is limited by the size of the motor.

It should be also noted that obviously an exposure can be released only when the desired heating current is reached so that the correct X-ray tube current must be set immediately at the beginning of an exposure.

An object of the present invention is the provision of an X-ray diagnosis apparatus of the described type wherein the transmission time period from illumination to exposure is substantially diminished as compared to prior art.

Other objects of the present invention will become apparent in the course of the following specification.

The present invention is based in part on the consideration that in many cases it is not necessary to wait with the release of an exposure until the rotary anode has reached its highest speed but that it is possible to release an exposure already when the speed of the rotary anode has reached during the high run a value permitting the exposure current.

Thus the objects of the present invention may be realized through the provision of means releasing an exposure during the high run of the rotary anode when the lowermost speed of the anode at which the exposure current of the X-ray tube is possible, and the desired heating current of the X-ray tube have been reached.

In accordance with the present invention an exposure is only then released at the highest speed of the rotary anode when the maximum permissible exposure current has been set. In all other instances the release of an exposure takes place already at an anode speed which is less than the highest speed so that the transmission time period between an illumination and an exposure always has the smallest possible value.

An advantageous further embodiment of the present invention is characterized by the provision of a calculator for determining the exposure current and thus the rated value of the anode speed and of the heating current of the X-ray tube at which an exposure is released. This determination takes place from the illumination data and the set exposure time period, as well as comparison means for the rated and actual value, whereby an exposure can be released when the rated and actual values correspond. This embodiment of the present invention has the advantage that the setting of the expo- 2 sure data is limited to the setting of the X-ray tube voltage and the exposure time, and possibly tothe selection of the focus, since the X-ray tube current'is automatically determined. V

A further advantageous embodiment of the present invention consists of a device actuated by the calculator for automatically changing the illumination data corresponding to the difference between the anode speed determined by the calculator and the highest anode speed when the speed determined by the calculator is greater than the highest anode speed. In that case an exposure is released only when the required anode speed resulting from the exposure current produced by the illumination data, would be greater than the highest speed.

The invention will appear more clearly from the following detaileddescription when taken in connection with the accompanying drawing showing the embodiment of the present invention.

In the drawing:

FIG. 1 shows the circuit of an X-ray diagnosis apparatus for feeding an X-ray tube with a rotary anode according to the present invention, and

FIG. 2 is a circuit illustrating a design of a time switch shown in FIG. 1.

In FIG. 1 is shown a rotary anode X-ray tube 1, which irradiates a patient 2 and by means of an image ampli' fier 3 produces radioscopic images. Near the output fluorescent screen of the image amplifier 3, an actual value transmitter 4 is arranged, which furnishes on line 5 a signal corresponding to the actual value of the image brightness on the output screen of the image amplifier 3, and hence to the actual value of the dose rate of the X-ray tube 1. The actual value transmitter 4 may be, for example, a photomultiplier or a photo-electric cell. The output signal of the actual value transmitter 4 is supplied to one input of a proportional-integral controller 6. To the input 7 of the proportional-integral controller 6 there is supplied,for the stabilization of the image brightness on the output screen of the X-ray image amplifier 3, a signal which corresponds to the nominal value of the dose rate and which is tapped by a nominal-value selector 8. At the output 9 of the proportional-integral controller a signal is available which is constant as long as the brightness on the output screen of the image amplifier 3 is constant. As soon as this brightness increases, also the output signal of the proportional-integral controller 6 increases. This output signal controls a regulating transistor 10 applied to dc voltage in series with a resistor 11. At resistor 11 two voltages are tapped, of which one controls via a switch 12 a transistor 13 and the other via a switch 14 a regulating triode 15.

Transistor 13 is provided in a diagonal of a diode bridge 16 and permits setting the effective value of the heating current of the X-ray tube 1. The heating current is furnished by a heating transformer 17, which is connected to two phases of the three-phase supply network.

The high voltage of the Xray tube l is generated by a three-phase high voltage transformer with three primary windings l8 and three secondary windings 19. The one end of the secondary windings 19 is connected to a high-voltage rectifier 20 which feeds the X-ray tube 1, and the other ends to a high-voltage rectifier 21 in whose direct current branch lies the regulating triode 15. The resistance between the anode and the cathode of theregulating triode 15'thus determines the high 3 voltage at the X-ray tube 1. This resistance is adjustable by the grid bias tapped at resistor 11.

lt-results that the X-ray tube current and X-ray tube voltage are determined by the base voltage of transistor 10. During radioscopy of the patient 2, the signal on line 9 which represents the base voltage of transistor 10 adjustsitself so that the brightness on the output screen ofthe image amplifier 3 is maintained constant. For the regulation of this brightness the X-ray tube voltage and X-ray tube current are'controlled. During radioscopy switches '12and 14 occupy their shown positions and one switch 24 is closed, sothat relay 25 is energized and closes its contacts 26.

To make a radiograph, the X-ray tube voltage is determined by a setter 73. Also the exposure time is set on a time switch 28. To change over from radioscopy to radiography, switch 14'is moved to its dashed position andswitch 24is opened, so that relay 25 opens its contacts 26. Switch is closed. Through switch 30 a feed device for motor 31, which drives the rotary anode of the X-ray tube 1, is taken into operation, said device consisting of a rectifier 32 and an inverter 33. The feed frequency of the rotary anode motor 31 is higher than the line frequency. w

With the rotary anode motor 31 is coupled a tachogenerator 34 or opto-electronic tachometer which furnishes on line 35 a signal which corresponds to the speed of the rotary anode motor 31. This signal is supplied to a comparator 36 at the input 37. At input 38 of comparator'36 a signal generated by acomputer 39 is a vailable'which corresponds to the lowest anode speed atwhi'ch the radiographic current is permissible. At the output 40 of computer 39 a signal is available which corresponds to the heating current of the X-ray tube 1 required for the radiographic current.

At input 41 there is supplied to computer 39 a signal which is equal to the output signal of the proportionalintegral controller 6 and thus embodies the transparency of the patient 2. At input 42 a signal is available which corresponds to the set exposure time. To input 43 is supplied a signal which corresponds to the radiographic voltage selected at the setter 73. From its input signals the computer 39 forms the mentioned output signalsfie; on line 38 a signal which embodies the lowest anode speed at which the radiographic current is permissible, and on line 40 a signal which characterizes the radiographic current. For this purpose there is stored in computer 39 the response of the lowest anode speed at which the radiographic current is permissible, as a function of the radiographic current. Further the computer is programmed according to the linkage of the radioscopy data with the exposure time and the radiographic X-ray tube voltage for the determination of the radiographic current. For the radiographic current 1,, there applies:

A isthe X-ray radiation dose required for a picture, determined by the signal at input 43; B is the dose rate; 1,,

- is the X-ray tube current during the radioscopy preceding the exposure; and la is the exposure time. The signal atinput 41 embodies the quantities B and I,,, and the signal at input 42 embodies-t0.

The time switch 28 is controlled by an UND gate 44, which has three inputs 45 to 47. lnput 45 is connected with the output of comparator 36, which compares the signal at input 38 corresponding to the lowest anode speed at which the radiographic current is permissible with the signal at input 37 embodying the actual value of the anode speed. Input 47 of the UND gate 44 is con nected to a comparator 48 which compares the signal at output 40 of computer 39, that is, the signal corre sponding to the nominal value of the heating current during the exposure, with a signal corresponding to the actual value of the heating current, which signal is present between the lines 49 and is tapped at a resistor 50 in the heating circuit. Input 46 of the UND gate 44 as well as the comparators 36 and 48 are controllable by a radiography switch 51, which is closed for the taking of a picture.

To make a radiograph, which can be done for example in known manner, by means of a camera 52 connected before the image amplifier 3, switches 30 and 51 are closed and switches 12 and 14 switched to their position shown in dashed lines. The determination of the radiographic current of X-ray tube 1 occurs by the signal at output 40 of computer 39 via the switch 12 switched during an exposure to its dashed position. The comparator 36 now continuously compares the constant signal at its input 38, which corresponds to the lowest anode speed at which the radiographic current determined by computer 39 is permissible, with the variable actual-value signal at input 37. As soon as these two signals are identical, it supplies to input 45 of UND gate 44 a signal marking the release of an exposure. Input 46 receives a similar signal from the closed switch 51. When comparator 48 supplies to input 47 a signal which marks that the radiographic X-ray tube current calculated by computer 39 has been reached, the exposure is released via the time switch 28 and relay 25, that is, relay 25 is energized by time switch 28 and closes its contacts 26. After the exposure time has run out, which is set on the time switch 28, the latter terminates the exposure.

The design of the time switch 28 is evident from FIG. 2. Input 56 of time switch 28 leads to a switching transistor 57 which actuates relay 25 via line 55. As soon as the UND gate 44 furnishes a start signal for an exposure, switching transistor 57 is switched to its lowresistance state and energizes relay 25 via contact 58 which is closed at first. Contact 58 can be actuated through a winding 59, which is controlled by a transistor 60. Transistor 60 is connected at the output of an operation amplifier 61, to whose positive input a constant voltage U is supplied and to whose negative input a voltage is supplied which is generated by an RC member 81. The exposure time can be set by a charging resistance 62.

As soon as UND gate 44 supplies on line 56 a start signal for an exposure, capacitor 81 is charged via the charging resistance 62. When the voltage U has been reached at the negative input of the operation amplifier 61, the latter trips and switches transistor 60 to its lowresistance state, so that winding 59 is energized and opens contact 58. The exposure is thereby ended. Therefore, the exposure time is adjustable by the magnitude of the resistance 62 which determines the charging of capacitor 81, and hence by tap '63.

The output signal of time switch 28, which characterizes theexposure time and is connected to the input 42 of computer 39, is accordingly tapped at resistance 62, i.e. between points 64 and 65.

According to the present invention, instead of the relay 25 in the primary circuit of the high-voltage transformer, the regulating triode may alternatively be used for switching an exposure on and off, if for this purpose a corresponding grid bias is applied to it.

An essential feature of the present invention is that the two comparators 36 and 48 bring about the release of an exposure when, on the one hand, the heating current of the X-ray tube required for the radiographic current and, on the other, the lowest anode speed at which the radiographic current is permissible are attained. An exposure is therefore always released already when the anode speed of the X-ray tube 1 has the minimum value which corresponds to the radiographic current for the X-ray tube determined by computer 39. The transition time from radioscopy to radiography is therefore always as short as possible. The difference between the X-ray diagnosis apparatus of the present invention and prior art therefore is that in prior art the transition time between radioscopy and radiography, insofar as it is determined by the acceleration time of the rotary anode of the X-ray tube, is constant, while in the X-ray diagnosis apparatus of the present invention, it is variable and always has its smallest possible value.

According to the present invention it is not necessary that the radiographic current be determined by a computer. Alternatively, the X-ray tube voltage, X-ray tube current, and time for an X-ray exposure may be set individually. But the described X-ray diagnosis apparatus has the advantage of simple handling. For the manual setting of the X-ray current for a radiograph, a setter 27 may be provided which determines the radiographic current when switch 12 connects line 70 with line 71.

6 In that case the negative input of comparator 48 must be connected at setter 27, and computer 39 is required only to determine that minimum anode speed at which the radiographic current is permissible. The connection between point 72 and computer 39 is therefore unnecessary in this case.

What is claimed is:

1. An X-ray diagnosis apparatus, comprising an X-ray tube with a rotary anode, a motor connected with said anode for driving it, means connected with said tube for determining its exposure time, means supplying a filament and exposure current to the Xray tube, means connected with the firstmentioned means for permitting an exposure during the high drive of the anode at its lowermost speed at which the exposure current is permissible and the desired filament current has been reached, the last-mentioned means comprising comparator means connected at its output with the means for determining the exposure time and having actual value and nominal value inputs, which are connected with actual value pick-ups and nominal value selectors for the filament current and the anode speed respectively.

2. An X-ray diagnosing apparatus according to claim 1, wherein the inputs of the comparator means being connected with the output of a computer for determin ing the exposure current and thus the nominal value of the anode speed and the filament current of the X-ray tube at which an exposure is released from a signal, which embodiesthe transparency of the patient and the set exposure time. 

1. An X-ray diagnosis apparatus, comprising an X-ray tube with a rotary anode, a motor connected with said anode for driving it, means connected with said tube for determining its exposure time, means supplying a filament and exposure current to the X-ray tube, means connected with the first-mentioned means for permitting an exposure during the high drive of the anode at its lowermost speed at which the exposure current is permissible and the desired filament current has been reached, the last-mentioned means comprising comparator means connected at its output with the means for determining the exposure time and having actual value and nominal value inputs, which are connected with actual value pick-ups and nominal value selectors for the filament current and the anode speed respectively.
 2. An X-ray diagnosing apparatus according to claim 1, wherein the inputs of the comparator means being connected with the output of a computer for determining the exposure current and thus the nominal value of the anode speed and the filament current of the X-ray tube at which an exposure is released from a signal, which embodies the transparency of the patient and the set exposure time. 